Chapter 6-2 Lewis Structures (p. 206 – 207)

Multiple Bonds A double bond is when atoms share two pairs (4 total) of electrons A triple bond is when atoms share three pairs (6 total) of electrons

Diatomic Molecules Gases that exist as diatomic molecules are H2, O2, N2, F2, Cl2, Br2, I2 octets          N  +  N   N:::N   triple bond

Drawing Lewis structures for molecules 1. Determine the total number of valence electrons in the molecule. 2. The atom with the lowest electronegativity is often the central atom (usually written first in the chemical formula). Arrange the other atoms’ symbols around the central atom. 3. Distribute eight electrons around each atom except hydrogen. If there aren’t enough e- to go around, form double or triple bonds. 4. Compare the number of valence electrons used in the structure with the number available from step 1. 5. Change each pair of dots that represents a shared pair of electrons to a single dash.

CO2 atom # of valence electrons per atom total # of valence electrons # of covalent bonds that atom can form C 4 2O 6 12 2 # of covalent bonds that atom can form = 8 - # of valence electrons per atom

Drawing Lewis Diagrams CO2 1 C × 4e- = 4e- 2 O × 6e- = 12e- 16e- O C O - 8e- 8e-

O C O Carbon dioxide Each atom can count all the electrons in the bond 8 valence electrons O C O

O C O Carbon dioxide Each atom can count all the electrons in the bond 8 valence electrons O C O

O C O Carbon dioxide Each atom can count all the electrons in the bond 8 valence electrons O C O

Draw the Lewis diagram for the following: HCN H2CO

HCN H N C H C N

H2CO H O C H H C O H